In a system that carries out movement observation of cars based on car images taken by a camera provided on a road, it has been carried out that a registration number of the car and a body color of the car are identified from the car images, and the cars to be searched is narrowed by comparing the registration number of the car and the body color of the car with a predetermined database. In addition, for example, JP-A-2000-222673 discloses a technique to identify the body color of the car from the color image in which the car is photographed, and narrow the cars to be searched based on the registration number of the car and the body color of the car.
However, when the car image is a color image, it is possible to identify the registration number of the car and the body color of the car as described above. However, when the car image is a monochromatic image or a color image photographed in the night (here, a color image photographed in a state where sufficient brightness cannot be secured), the registration number of the car can be identified, but the body color of the car cannot be identified. Therefore, in the night, it was impossible to narrow the cars to be searched by the body color of the car. Incidentally, in the aforementioned publication, by providing the light, which synchronizes with the shutter of the camera, the sufficient brightness is secured even in the night or in a dark place such as the underground to identify the body color of the car. However, only the brightness in a level that the body color of the car can be identified is secured, and this publication does not indicate any technique to presume the body color of the car from the monochromatic image or the color image photographed in the night.
In addition, for example, JP-A-2005-111852 discloses an image conversion technique from the monochromatic image to the color image. Specifically, a technique is disclosed that, in a copy machine, in a case where a print request of a color image is received even when a document is a monochromatic image, the monochromatic image is printed as a color image based on a small storage medium attached to the document. However, this is not a technique to presume the colors from the monochromatic image.